The subject invention is directed to an ignition distributor rotor and, more specifically, to an ignition distributor rotor having at least one electrical conductor member in electrical contact with the electrically conductive rotor segment and the electrically nonconductive rotor body radially inwardly from the output tip of the rotor segment and extending radially outwardly toward the output tip in a manner to define a terminating point.
Most modern internal combustion engine ignition systems contain two arc gaps in the secondary circuit of the ignition coil, the distributor rotor gap between the distributor rotor segment output tip and the distributor cap output terminal with which it is in register and one of the spark plugs. It is well-known that a primary source of automotive radio frequency interference is the large fast rise time impulsive current which flows at the onset of electrical breakdown of both the distributor rotor gap and the spark plugs. When the ignition coil primary winding energizing current is interrupted, the ignition coil secondary output, v(t), decreases nearly linearly from zero at the rate of 10.sup.9 volts per second. In an ignition circuit, v(t) appears almost entirely across the distributor rotor gap prior to the breakdown of this gap. It has been learned that the controlling factor in determining the breakdown voltage for a given distributor rotor gap geometry is the supply of electrons to start the breakdown process leading to arc formation and that an inadequate supply of initiatory electrons leads to high breakdown voltages. In general, an inadequate supply of initiatory electrons creates faster rising time pulses of increased magnitude through the distributor rotor gap, a condition which increases radio frequency interference radiation.
The initiation of distributor rotor gap breakdown depends only upon v(t). Changes in the circuit which do not alter v(t) prior to breakdown cannot be expected to alter the breakdown voltage. For a given circuit and distributor rotor gap geometry, it is generally observed that the larger the breakdown voltage, the larger will be the resulting di/dt and radio frequency interference. With a fixed direct current potential applied across the distributor rotor gap, the conduction of electricity across the distributor rotor gap takes place by the transport of free electrons and ions. An initiatory electron, the first free electron to appear in the distributor rotor gap, is accelerated by the applied electric field and collides with the individual molecules of the air within the distributor rotor gap. There is a certain mathematical probability that these collisions will result in ionization which leads to electron multiplication. This probability may be expressed as the average number of ionizing events per electron per unit length of drift in the direction of the applied electric field. This quantity is a function of E/t where E is the applied electric field and t is the gas pressure within the distributor rotor gap. Because of their much greater mass, the ions produced are left behind the advancing electron avalanche. To form an arc in the distributor rotor gap capable of carrying the required spark plug arc current at low distributor rotor gap voltages, the electron and ion densities in the distributor rotor gap must be increased far beyond that produced by a single avalanche. To achieve multiple avalanches leading to an arc, the initiatory electron must be replenished before the avalanche reaches the positive electrode. Nothing can happen until the initiatory electron appears. The supply of initiatory electrons is a limiting factor in reducing the implusive breakdown found in the distributor rotor gap. Because of the rapid fall of the ignition coil secondary winding output, the potential across the distributor rotor gap is at or slightly above the direct current breakdown potential for only a very short period of time. When the applied voltage V is greater than the direct current breakdown voltage V.sub.B, the distributor rotor gap is said to be overvolted. The overvoltage is defined as a ratio V/V.sub.B.
If an initiatory electron is not present while the overvoltage is low, the coil output will continue to fall until the applied electric field becomes sufficiently intense to produce the initiatory electron, presumably by electron emission from the rotor segment. It is not uncommon to observe overvoltage ratios of 2:5 in distributor rotor gaps. In this event, the multiplication of the initiatory electron is enormously enhanced. Hence, the avalanche forms much more quickly and with more rapid electron multiplication under these highly overvoltage conditions which, in turn, leads to a more rapid rise in arc current flow through the distributor rotor gap and associated circuitry and to increase radio frequency interference. Therefore, an ignition distributor rotor of the type which produces a large corona effect for efficiently injecting electrons into the distributor rotor gap which serve as initiatory electrons is desirable.